In recent years, attention has been focused on a technique, e.g., for separating, synthesizing, extracting, and analyzing a trace amount of reagent using a micro-reactor made up of a microchip, which includes a micro-scale analyzing channel formed by the semiconductor micromachining technique on a small substrate that is composed of silicon, silicone, or glass.
A reaction analysis system employing such a micro-reactor is referred to as a micro total analysis system (hereafter referred to as the “μTAS”). According to the μTAS, for example, the ratio of surface area to volume of the reagent is increased, thereby enabling reaction analysis to be performed at high speeds with high precision and implementing a compact automatized system.
The microchip may be provided, in a flow path also called a microchannel, with regions having various types of functions such as a reaction region in which a reagent is disposed, thereby constituting a chip suitable for various uses. The representative uses of the microchip may include analyses in the fields of chemistry, biochemistry, pharmacy, medicine, and veterinary medicine, such as genetic analysis, clinical diagnosis, and drug screening; synthesis of compounds; and environmental measurements.
The aforementioned microchip is typically constructed to have a pair of substrates which are opposed and adhered to each other, with a fine flow path (e.g., approximately ten to a few hundreds of micrometers in width and ten to a few hundreds of micrometers in depth) formed on a surface of at least one of the substrates. The microchip has been constituted mainly of a glass substrate because the glass substrate can be manufactured with ease and permit optical detection. Furthermore, recently, such a microchip has been under development which employs a resin substrate that is lighter, more inexpensive, and more resistant to damage than the glass substrate.
For microchips, bonding may be thought to be performed by means of adhesive or by heat fusion. However, both the methods are not preferred for the following reasons.
The use of adhesive would cause the adhesive to exude to the micro flow path, thereby blocking the flow path, narrowing part of the micro flow path so as to make the flow path uneven, and causing disturbances in the homogeneous characteristics of the wall surface of the flow path.
Furthermore, in the case of the heat fusion, fusion at a thermal melting point or higher would cause, for example, the flow path to be collapsed at a heating stage or the flow path not to be retained in a predetermined cross-sectional shape. Thus, the adhesion by heat fusion would cause a higher performance microchip to be implemented with difficulty.
In this context, in recent years, there has been a more general method in which a surface of substrates is irradiated with vacuum ultraviolet light so as to activate the substrate surface, and then the substrates are bonded together.
For example, proposed in Patent Literature 1 is a method which is used to bond a plurality of microchip substrates made of a resin, the method being configured, for example, such that a substrate surface of at least one of two resin substrates made of, e.g., cyclo olefin polymer (COP) is irradiated with light from an excimer lamp having an emission line at a wavelength of 172 nm; and then both the substrates are stacked one on the other so as to be heated to a temperature less than a plastic deformation point, or alternatively to join both the substrates together by applying pressure thereto without heating the substrates.
Furthermore, proposed in Patent Literature 2 is a method for irradiating a respective surface of two resin substrates made of, e.g., COP with vacuum ultraviolet light at a wavelength of 172 nm so as to heat the substrates while the irradiated surfaces are in contact with each other, thereby adhering the substrates together. Note that the heating step may also be performed while force is being applied to the substrates in a direction in which the surfaces are brought into intimate contact with each other.
Furthermore, proposed in Patent Literature 3 is a method for irradiating a respective surface of two resin substrates made of, e.g., COP or PMMA (Polymethyl methacrylate) with vacuum ultraviolet light at a wavelength of 172 nm and then allowing the irradiated surfaces to be stacked one on the other, so that both the substrates are adhered together while both the substrates are being pressurized.